Cathode-ray tube direction finder



H. E. RHEA July 8, 1947.

CATHODE RAY TUBE DIRECTION FINDER Filed Nov. 27,1945 2 sheets-sheet l wwww5 www u E mm mum .l s@ EN@ En@ 4 E H `mM\ m W &1 w .wmw w wwwQnvkwfvl` NN mxmbk w.

July 8, 1947.

H. E.RHEA

CATHODE RAY TUBE DIRECTION FINDER 2 sheets-'sheet 2 Filed NOV. 27, 1943(Itiotneg Patented July 1947 STES CATHODE-RAY TUBE DIRECTION FINDERHenry E. Rhea, Collingswood, N. J., assigner to Radio Corporation ofAmerica, a corporation of Delaware Appiicatien November 27, 1943, SerialNo. 512,028

11 Claims. l

My invention relates to cathode ray indicator systems and particularlyto systems for indicating the position of an object with respect to aradio transmitter.

The invention will be described specifically as applied to a pulse-echosystem wherein the transmitter radiates signals from antennas havingoverlapping directional radiation patterns, the indicator functioning togive the position of the said object with respect to the radiationpatterns, and particularly to inform an operator when the object islocated within the equi-signal region oi the overlapping patterns.

An object of the invention is to provide an improved indicator fordirection iinding or object locating apparatus.

A further object of the invention is to provide an improved cathode rayindicator system for indicating the position of an object with respectto overlappingradiation patterns.

A still further object of the invention is to provide an improvedindicator for radio pulse-echo apparatus.

In a preferred embodiment, the invention is applied to a pulse-echosystem having a directive antenna system so designed that its radiationpattern or patterns may be rotated in both a horizontal plane and avertical plane to search for an object such as an enemy airplane. Theantenna system may consist of four directive antennas which may be keyedsuccessively, as described, for example, in application Serial No.259,057, filed February 28, 1939, Patent No. 2,412,702, granted December17, 1946, in the name of Irving Woli, and entitled Object detection andlocation, o-r an antenna system may be employed which is keyed by meansof shorting condensers as described and claimed in application SerialNo. 412,943, filed September 30, 1941, Patent No. 2,400,736, granted May21, 1946, in the name of George H. Brown, and entitled Antenna systems.

In the receiver, the vertical deflecting plates of a cathode ray tubehave applied to them, during the right and left antenna switchingperiods, the received pulses that have been reflected from the target orother object. A square Wave deflecting voltage corresponding to thediiierence in amplitude between the right and lef pulses is applied tothe horizontal delecting plates. This square wave may be obtained from apeak voltage measuring circuit that is switched in synchronism with thekeying of the directive antennas. Thus, the amplitudes of the rightleftvertical deiiecting traces of the cathode ray are determined by therelative amplitudes of the (Cl. Z50- 1.72)

2 reilected pulses in the two horizontal radiation patterns and thehorizontal deection, and thus the spacing between the vertical traces isdeter mined by the difference in amplitude of the right- 5 left pulsesin the horizontal radiation patterns.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Figure l is acircuit and block diagram of one l of the preferred embodiments of myinvention,

Figure 2 is a diagram of the radiation patterns of the right-leftdirective antennas employed in the system of Fig. 1.

Figure 2a is a View representing received radio pulses afterdemodulation in the receiver of the system of Fig. l,

Figures 3 to 3d are views of the screen end of the cathode ray tubeemployed in the system of Fig. 1 showing the position of the cathode rayspot for different relative positions of the transmitter radiationpatterns and the object or target,

Figure 4 is a circuit and block diagram of another embodiment of myinvention,

Figures 4a to 4d are views of the screen end of the cathode ray tubeemployed in the system of Fig. 4 showing the cathode ray trace fordifferent positions of a target or the like with respect to the. tworadiation patterns in the hori- 30 zontal plane, and

Figures 5 to 5c are views corresponding to Figs. 4a to 4d, respectively,for a modification of the system shown in Fig. 4.

In the several figures, similar parts are indicated by similar referencecharacters.

In Fig. 1, my indicator is applied to a radio pulse-echo systemcomprising four directive antermas I 0, i2 and I3 for radiating up,down, right and left patterns, respectively, as indicated by the lettersU, D, R and L. The radiation patterns for these antennas are conicalApatterns that overlap as indicated in Fig. 2 where the patterns markedR and L correspond to the antennas similarly marked in Fig. 1. Theantennas Iii, Il, l2 and I3 may be like those illustrated in theabove-mentioned Wolff application, or of any other suitable type.

High frequency radio pulses are supplied successively to the U, R, D andL antennas from a 50 transmitter I3 through cam operated switches Il,I8, I9 and 2|, respectively, driven by a motor 22. The said pulses areobtained by modulating the high frequency carrier wave produced attransmitter I6 by means of keying pulses -frorn a source 23. The source23 may be a multivibrator suppyling pulses recurring at the rate of 4.1kilocycles per second, for example.

The receiver 26 demodulates the 4.1 kc. pulses of high frequency energyto supply 4.1 kc. video frequency pulses (shown in Fig. 2a) to arightleft switch 3! and to a rectiiier 25 which preferably is of thepeak rectifying type. The switch arm 3| is moved by a cam 32 intoContact with the upper and lower switch points (indicated at R and L,respectively) during the right and left switching periods, respectively,whereby the video frequency pulses corresponding to these periods areapplied through an amplifier 36 to the vertical deecting plates 3l ofthe cathode ray tube S8. In the circuit illustrated, the rectifier 26 isa grid-leak biased peak rectifier tube which is well known in thetelevision art. The output of the rectifier 25 is passed through a lowpass filter 25 and supplied through a large capacity blocking condenser35, through resistors 5 and 6, to cam operated switches 2B and 23, whichapply right-left pulses to condensers 33 and 34, respectively. A leakresistor for the several condensers is shown at The resistors 5 and 6are provided to make the time constant of the condenser circuits longenough to smooth out and substantially eliminate the effect of any highfrequency noise pulses that may be received. The output from the lter 25is represented by the graph 5l where the four groups of filtered orintegrated 4.1 kc. Video frequency pulses of unequal amplitude areindicated at U, R, D, L.

An amplifier tube L39 has its input electrodes connected acrosscondensers 33 and 34 alternately by a switch 4l whereby the signaloutput of the tube corresponds to the charges on the condensers 33 and34 to produce the square wave 42 so long as the reflected right-leftpulses diier in amplitude. The anode of the tub-e di) is connected tothe horizontal deiiecting plates 43 of the cathode ray indicator tube 38through a capacitor 8. A resistor 9 permits a charge to leak off thecapacitor 8.

The cam switches 29, 29, 4l and 3l are driven in synchronism with theantenna switches Il, I8, I9 and 25 by the motor 22. Thus, when the rightantenna switch 8 is closed. the corresponding right switch 28 of theindicator is also closed. Likewise, the switch 4l is closed in its upperposition and will remain closed until the left switches 2) and 29 close,whereby the square wave i2 is produced. The R and L cycles of the wave42 approach the A.C. axis to become a straight line (zero square wave)when the right-left radiation patterns are symmetrical with respect toor on the target. Also, when the right antenna switch it is closed, theswitch 3| is in its upper position. Thus for the condition shown in Fig.2a, the cathode ray is deflected and held to the right by the R cycle ofthe wave 42 and deflected vertically with large amplitude by the 4.1 kc.pulses applied through the switch 3E. Next, as the cams are rotatedthrough 180 degrees, the switches 2] and 29 close and the switches lland 3l move to their lower positions.

The cathode ray is now deflected and held to the left by the L cycle ofthe wave 62 and deected vertically with small amplitude by the 4.1 kc.pulses applied through the switch 3 l. Therefore, the right-leftindication is as shown in Fig. 3a. The switching sequence in thisparticular example is U, R, D, L as will be apparent from the shape ofthe cams and from the direction of rotation indicated by the arrows. Thecomplete switching cycle may occupy 1/en second, for example.

The particular graph shown in Fig. 2a represents a condition where theradiation pattern of the antenna system is not centered on the target.It will be noted that the reflected pulses during the interval U are ofless amplitude than during the interval D, and that during the intervalR they are of greater amplitude than during the interval L. During thetime switch Z8 is closed, the condenser 33 is charged to a voltage equalto the peak voltage of the R group oi reflected pulses; after switch 2Sopens, condenser 33 retains this charge. When switch 28 next closes, thecondenser 33 either acquires more charge or loses some charge if thepeak amplitude of the pulses has changed. Similarly, the condenser 34 ischarged by the received pulses so that the voltage thereacrosscorresponds to the peak amplitude of the pulses in group L. The switches23 and 29 preferably are timed to close shortly after the beginning ofintervals R and L of graph 5l, respectively, and to open shortly beforethe end thereof. This prevents any error that might otherwise resultfrom an unlike number of 4.1 kc. pulses in the R and L groups.

In an indicator of the character being described, it is important toavoid any possibility of a false reading resulting from lack of incomingsignal. This possibility is avoided with the circuit of Fig. 1 since theindication becomes a spot on the iiuorescent screen of the tube 3B asshown in Fig, 3d if there is no incoming signal.

From the foregoing, it will be understood that in Figs. 3 to 3e thedifferent positions and Vlengths of the cathode ray traces give thefollowing information: Fig. 3 indicates that the object or target is tothe left of the center line of the transmitter radiation pattern; Fig.3a indicates the target is to the right of the point aimed at; Fig. 3bindicates the target is nearly on center horizontally; and Fig. 3cindicates it is on center; that is, the antenna right-left radiationpattern is now on the target. If the incoming signal disappears for anyreason, the only indication is a spot as shown in Fig. 3d.

One important feature of my indicator system is that the transmitterradiation pattern can always be centered on a target regardless ofVariations in the incoming signal strength since such variations willproduce the same percentage change in all the voltages on the deectingplates. It may be noted that while the use of a peak rectifier such asrectifier 26 is preferred, it is possible to employ other rectiers suchas one having an output that is a measure of the area or power of apulse.

It will be understood that an indicating system similar to the onedescribed above may be employed for the up-down indications.

In Fig. 4 there is shown an embodiment of the invention that givesleft-right indications of the character shown in Figs. 4a to 4c. Theleft-right horizontal deflections of the cathode ray are obtained aspreviously described.

The vertical trace is obtained by applying to the deecting plates 3l asine wave 55 that has an amplitude proportional to the signal strength.This may be done by supplying a voltage from the 60 cycle line over aconductor 52 to the deflecting plates 3'! through an amplifier 53. Thegain of the amplifier 53 is controlled in accordance with the strengthof the incoming signal by means of an automatic volume control circuitcomprising a diode 54 connected to the output of the receiver V24. Sincethe motor 22 drives the cam operated switches synchronously with the 60cycle power area51@ supply, the "R and L cycles of the sine wave 55 andof thesquare wave 42 will occur simultaneously. In the example shown,the cathode ray is deflected up by the R cycle of the sine wave 55 anddown by the L cycle. The down deflection preferably is masked olf asindicated at 56 on the drawing.

The position of the vertical trace 65 above the mask 56 depends upon theamplitude and phase of the square wave 42 with respect to its A.C. axis;these, in turn, depend upon the relative amplitudes of the receivedpulses during the right and left switching periods. The amplitude ofwave 42 becomes zero when the pulses of periods R and L become equal inamplitude as they do when the antenna radiation patterns come to the ontarget position. The phase of the wave 42 reverses when the radiationpatterns swing past the on target position. Therefore, as shown in Figs.4a to 4c, the vertical indicating trace 65 appears on the uorescentscreen either to the right or to the left of center depending upon thephase of the square wave 42, and it moves closer to center as theradiation patterns are brought closer to the on target position. If thesignal fades away, the cathode ray indication is reduced to a spot asshown in Fig. 4d.

Figs. 5 to 5c show the type of indication that may be obtained bydifferentiating the square wave 42 before it is applied to the deectingplates 43. This may be done by giving the capacitor 8 a small capacityvalue so that only the high frequency components of the wave 42 arepassed. The sine wave 55 is then phased with respect to the wave 42 sothat the pulses of the differentiated wave occur at the instant the wave55 has a suitable amplitude (an amplitude other than zero) with respectto its A.C. axis. The resulting indication is a spot 66 that is producedduring the occurrence of the differentiated wave pulse that occursduring the sine wave cycle that deects the cathode ray upwardly.

I claim as my invention:

1. In a radio pulse-echo system, a plurality of directive antennashaving overlapping radiation patterns in a certain plane, a radio pulsetransmitter unit and a radio pulse receiver unit, means for switchingsaid antennas successively to at` least one of said units, a cathode raytube indicator having a pair of horizontal deflecting elements and apair of vertical deecting elements, means for obtaining a rectangularwave having a peak-to-peak amplitude that is a measure of the relativeamplitude of the two groups of reflected pulses in said plane, means forapplying said rectangular wave to one pair of said deflecting elements,and means for applying to the other pair of deflecting elements adeflecting voltage which is in synchronism with said signal wave.

2. An indicator for a radio pulse-echo system of the type comprising aplurality of directive antennas having overlapping radiation patterns ina certain plane, a radio pulse transmitter unit and a radio pulsereceiver unit, means for switching said antennas successively to atleast one of said units, said indicator comprising a cathode ray tubehaving a pair of deflecting elements, means for obtaining an electricalwave that is a measure of the relative amplitudes of the two groups ofreected pulses in said plane, means for applying said wave to said pairof deecting elements to deflect the cathode ray of said tube to oppositeextreme positions, and means for deecting said cathode ray substantiallyat right angles to the deflection produced by said wave Wl 'um d whilesaid cathode ray is in said extreme positions" of deflection.

3. The invention according to claim 2 wherein said last means comprisesa second pair of deecting elements, and means for applying the reflectedradio pulses to said second pair of elements.

4. The invention according to claim 2 wherein said electrical wave is asquare wave.

5. The invention according to claim 2 wherein said electrical wave is aderivative of a square wave.

6. In a radio pulseecho system, a plurality of directive antennas havingoverlapping radiation patterns in a certain plane, a radio pulsetransmitter unit and a radio pulse receiver unit, means for switchingsaid antennas successively to at least one of said units. a cathode raytube indicator having a pair of deflecting elements, means for obtaininga square wave that is a measure of the relative amplitudes of the twogroups of reilected pulses in said plane, means for applying said squareWave to said pair of deflecting elements, and means for deilecting thecathode ralr of said tube substantially at right angles to and insynchronism with the deflection produced by said square wave.

7. In a radio pulse-echo system, a plurality of directive antennashaving overlapping radiation patterns in a certain plane, a radio pulsetransmitter unit and a radio pulse receiver unit, means for switchingsaid antennas successively to at least one of said units, a cathode raytube indicator having a pair of deecting elements, means comprising twostorage capacitors for obtaining thereacross two voltages, respectively,which are a measure of the amplitudes of the two groups of reflectedpulses in said plane, switching means for converting said two voltagesto a square wave that is a measure of the relative amplitudes of the twogroups of reflected pulses in said plane, means for applying said squarewave to said pair of deilecting elements, and means for deecting thecathode ray of said tube substantially at right angles to and insynchronism With the deflection produced by said square wave.

8. The invention according to claim 7 wherein said last means includes asecond pair of deflecting elements and wherein means is provided forapplying to said second pair of elements a deflecting voltage thatdecreases in amplitude in response to a decrease in the amplitude of thereceived signal.

9. In a radio pulse-echo system, a plurality of directive antennashaving overlapping radiation patterns in a certain plane, a radio pulsetransmitter unit and a radio pulse receiver unit, means for switchingsaid antennas successively to at least one of said units, a cathode raytube indicator having a pair of horizontal deflecting elements and apair of vertical deflecting elements, means for obtaining a square wavethat is a measure of the relative amplitudes of the two groups ofreflected pulses in said plane, means for applying said square wave toone pair of said deflecting elements, and means for applying said twogroups of reflected pulses to the other pair of deecting elements.

l0. In a radio pulse-echo system, a plurality of directive antennashaving overlapping radiation patterns in the horizontal plane and havingoverlapping radiation patterns in the vertical plane, a radio pulsetransmitter unit and a radio receiver unit, means for switching saidantennas successively to at least one of said units, a cathode ril raytube indicator having a pair of horizontal'defleeting elements and apair of vertical deflecting elements, means for obtaining a square wavethat is a measure of the relative amplitudesof the two groups ofreflected pulses in the horizontal plane, said last means includingswitching means operated in synchronism with said antenna switching,means for applying said square wave to said horizontal deflectingelements, and means for applying said two groups of reflected pulses tothe vertical deflecting elements.

11. In combination, means for transmitting radio signals and means forreceiving them after reflection from a reflecting object, at least oneof said means including an assembly of directive antennas havingoverlapping radiation patterns in a certain plane, switching means formaking said patterns effective successively to supply signal to areceiving circuit, said radiation patterns having characteristics suchthat the received signal diiers in strength for the successive radiationpatterns in accordance with the displacement of said radiation patternswith respect to said reiiecting object, a pair of capacitors included insaid receiving circuit, receiver switching means synchronized with theantenna assembly switching means, means comprising said synchronizedswitching means and said receiving means for charging each of saidcapacitors in accordance with the amplitude of the received signalduring the intervals that each of said radiation patterns, respectively,is effective to supply signal to the receiving means, a cathode ray tubeindicator having two pairs of deflecting elements that are angularlydisplaced with respect to each other, means for applying to one pair ofsaid deflecting elements a square wave having a peak-to-peak amplitudeproportional in amplitude to the Voltages across said capacitors, andmeans for applying a deflecting voltage to the other pair of delectingelements synchronous with said square wave.

HENRY E. RHEA.

